<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<input type="text" id="i1">
<input type="text" id="i2">
<input type="button" value="加" onclick="fn1(1)">
<input type="button" value="减" onclick="fn1(2)">
<input type="button" value="乘" onclick="fn1(3)">
<input type="button" value="除" onclick="fn1(4)">
<div>结果:0</div>
<script>
    function fn1(x) {
        let i1 = document.querySelector("#i1");
        let i2 = document.querySelector("#i2");
        let d = document.querySelector("div");
        //判断输入的内容不是数值时 提示信息
        if (isNaN(i1.value)||isNaN(i2.value)){
            d.innerText="输入错误!"
            return;
        }
        switch (x) {
            case 1:
                d.innerText = "结果:"+(i1.value*1+i2.value*1);
                break;
            case 2:
                d.innerText = "结果:"+(i1.value*1-i2.value*1);
                break;
            case 3:
                d.innerText = "结果:"+(i1.value*1*i2.value*1);
                break;
            case 4:
                d.innerText = "结果:"+(i1.value*1/i2.value*1);
                break;
        }
    }
</script>
</body>
</html>